1. Field of the Invention
The present invention relates to an image capture apparatus which can capture an image while controlling a light-emitting device to emit light.
2. Description of the Related Art
Various techniques for optimizing flash light emission control at a flash image capture timing of an image capture apparatus such as a camera or mobile phone have been proposed. Especially, many methods of determining a main light emission amount by preliminarily emitting flash light prior to an exposure operation, and measuring reflected light of the preliminarily emitted light from an object for a plurality of photometry areas have been proposed. This is because appropriate light emission amounts can be determined for various scenes by determining a main light emission amount by a predetermined algorithm based on photometry results of the plurality of photometry areas.
Japanese Patent Laid-Open No. 2005-275265 has proposed the following image capture method, so as to stably obtain an appropriate exposure amount. Ratios R(i) between photometric values P(i) of respective photometry areas immediately before preliminary light emission and photometric values H(i) of the respective photometry areas during preliminary light emission are calculated for respective photometry areas. A maximum one of the obtained ratios R(i) is extracted as a reference value baseR, and weighting coefficients W(i) for respective areas are determined by comparing the values R(i) of the respective areas with the reference value baseR. Reflected light amounts of the respective areas at the time of preliminary light emission are weighted and averaged according to the weighting coefficients W(i), and a main light emission amount is calculated based on the obtained weighted averaging result.
With the technique described in Japanese Patent Laid-Open No. 2005-275265, a value LVL0 corresponding to a maximum reflected light amount and a value LVL1 corresponding to a minimum reflected light amount at the time of preliminary light emission are calculated according to image capture distances to an object. Of photometry areas having luminance values D(i) of only reflected light components at the time of preliminary light emission, which fall within a range between the values LVL0 and LVL1, one having the maximum ratio R(i) is determined as a principal object area, and the ratio R(i) of that area is extracted as the reference value baseR. With this method, stable exposure amounts can be obtained in many normal scenes. In addition, even when an image in an identical scene is captured by slightly changing a composition, an image capture result with a small change in exposure amount can be obtained. As image capture distance information to an object, when an image capture lens has a distance encoder, that information is acquired based on the distance encoder information. However, when an image capture lens does not have any distance encoder, an empirically determined assumed distance is used.
When the image capture lens does not have any distance encoder, and when the assumed distance is largely different from a distance to a principal object, the ratio R(i) calculated from the reflected light amount from the principal object area cannot fall within the range between the values LVL0 and LVL1, and an appropriate exposure amount cannot often be obtained at an image capture timing. More specifically, when an image is captured in a state in which the distance to a principal object is smaller than the assumed distance, since the ratio R(i) of the principal object area becomes larger than the value LVL0, a weighting coefficient W(i) for that area is reduced. For this reason, the calculated main light emission amount of a light-emitting device is excessive for the principal object, and the principal object is overexposed consequently.